May told parliament earlier this year that McKinnon was too ill to be extradited and could pose a suicide risk if coerced. He was allowed to remain in Britain on human rights grounds.

"The potential difficulties in bringing a case in England and Wales now should not be underestimated, not least the passage of time, the logistics of transferring sensitive evidence prepared for a court in the US to London for trial, the participation of US government witnesses in the trial and the need fully to comply with the duties of disclosure imposed on the CPS," said Starmer in a statement.

McKinnon's mother Janis Sharp described the outcome as "amazing" and expressed her gratitude to May for her role in achieving it.

"Gary admitted to the intrusion, he always denied the damage. I feel the 10 years have been gruelling, it's been life-destroying. It's difficult to explain how bad it's been," BBC News quotes her as saying.

"To have this over is amazing. Gary's gone through enough. Other people have been accused of more serious hacking in this country, and they've been given a £1,000 fine and a very short community sentence.

"Gary regrets what he's done. He wishes he hadn't done it. He wishes he hadn't upset the Americans. We all regret it. But I'm grateful to Theresa May that this is all over now."

May announced plans to change extradition rules to allow the courts to block orders if it is in the interest of justice as a result of the McKinnon case.